The fan-filter unit of the invention is an air filtration device incorporating a centrifugal fan and a filter, and provides purified air to the space of a room. Fan-filter units have been widely used in the industry, medical and research facilities. They are especially popular for their characteristics of space-saving, energy-saving and easy installation. However, existing fan-filter units often generate high levels of noise in operation and may psychologically or mentally annoy the personnel within the room where precise and delicate manufacturing processes are being handled. Therefore, there is a need for a clean room fan-filter unit to operate and generate noise at a low level.
A fan-filter unit usually incorporates a centrifugal fan. The airflow drawn into the unit is guided by interior air passageways to the filter in the unit. After passing through the filter, the air is propelled into the designated environment, such as a clean room. The construction of the fan-filter unit makes less space in the axial direction of the fan than in the radial direction. The limited space increases the difficulty of incorporating noise reduction constructions into the fan-filter unit. For example, in a conventional fan-filter unit, for the airflow from the inlet to the outlet, the contact area of the airflow to some sound-absorbing materials is so limited that it performs low effectiveness.
People have been trying to solve the serious problem of the high noise levels of conventional fan-filter units. An exemplary prior art for reducing the noise of a clean room fan-filter unit is disclosed in U.S. Pat. No. 5,803,721. It provides a fan-filter unit having a perforated plate situated within the airflow path in the fan-filter unit housing such that the perforations diffuse the airflow before it passes through a filter and exits the housing. The uniform airflow provided by the perforated plate produces a reduced noise level.